1. Field of the Invention
The present invention relates to a surface treating apparatus for solid particles, a surface treating method therefor and a method for producing toner for developing an electrostatic charge image.
2. Related Background Art
Various methods for surface treatment of solid particles and powder treating apparatus have already been proposed. For example, powder treating apparatus of impact type utilizing a rotary blade and powder treating apparatus utilizing heat treatment are already known. The powder treating apparatus of impact type utilizing the rotary blade is described in Y. Takayama, Y. Kikuchi and K. Ono: "Zairyo Gijutsu" Vol. 8, No. 8, 10 (1990). There have been proposed methods for treating the surfaces of powder particles (as described in Japanese Patent Publication No. 42-27021 and Japanese Patent Application Laid-Open No. 7-244399), the method utilizing a hybridization system described in the Japanese Patent Application Laid-Open No. 62-83029 and already put on the market by Nara Kikai Co., Ltd., or an impact pulverizer described in Japanese Patent Publication No. 42-27021 and put on the market by Turbo Kogyo Co., Ltd.
In the hybridization system, for example, a treating apparatus as illustrated in FIGS. 12, 13 and 14 is used, wherein a casing 151, a stator 158, a stator jacket 177, a recycling valve 163, a discharge valve 159, a discharge valve 119 and a raw material charging chute 164 are shown.
In this apparatus, the powder particles and other fine solid particles charged from the raw material charging chute 164 are subjected, in an impact chamber 168, to instantaneous impact by two or more rotor blades 155 provided on a rotor 162 rotated at a high speed, and collide with a peripheral stator 158 to disperse in the system while breaking up agglomeration of the powder particles and the other fine solid particles, whereby the other fine solid particles are adhered onto the surface of the powder particles by electrostatic force or Van Der Waals force or, in case the powder particles alone are charged, such particles are subjected to rounding and formation of spherical particles. Such process proceeds with the flight and collision of the particles. Thus the particles are treated by plural passages through the recycle pipe 163, along the air flow caused by the rotation of the rotor blades 155. In addition, through the repeated impacts given by the rotor blades 155 and the stator 158, the other fine solid particles are uniformly dispersed and fixed on the surfaces, or the vicinity thereof, of the powder particles or, in case the powder particles alone are charged, the particles are shaped into a spherical form.
After such fine particle fixation, the particles are discharged through a discharge valve 159, controlled by a discharge valve control device 128, and a discharge chute 119 and collected by a bag filter 122 connected with a suction blower 124.
However such conventional powder treating apparatus requires the operation for a prolonged period, because the surface treatment of the powder particles is effected by the rotor blades 155 rotating at a high speed, utilizing the recycle pipe 163. Such operation may involve excessive collisions of the particles, leading to heat generation in the powder and eventually to denaturing thereof. In such apparatus, in order to achieve uniform surface treatment it is necessary to charge a predetermined amount of powder in a certain given volume and to execute a prolonged treatment ranging from several tens of seconds to several minutes. In such operation, because of the prolonged process time and of the high concentration of powder dust, re-agglomeration of the dispersed particles may occur in the course of surface treatment or the formation of fused solid matter may be formed by the generated heat.
The powder treating apparatus as shown in FIGS. 12 to 14, being a batch system, is incapable of continuous processing. For this reason, accessory equipment such as a weighing machine for weighing and charging a predetermined amount of the powder material into the treating apparatus, is required. Consequently such apparatus has been associated with drawbacks such as a high production cost and a narrow tolerance for the stable manufacturing operation.
Such drawbacks tend to become particularly conspicuous in the surface treatment of the solid toner particles for producing a toner used for developing an electrostatic charge image in a copying machine or in a printer.
Since, in general, various different properties are required for a toner, the characteristics of the toner are often affected by its producing method, in addition to raw materials used therefor. In the surface treating process of toner particles, it is required to produce toner particles with satisfactory quality in an efficient and stable manner at a low cost.
A binder resin used for toner particles is generally composed of a resinous material having a low melting point, a low softening point or a low glass transition point, and the toner particles containing such resinous material tends to cause fusing or adhesion to the surface treating apparatus in the surface treatment process.
On the other hand, for energy saving in the copying machine utilizing toner fixation with heat and pressure, binder resins having a low glass transition point or a low softening point came into use in order to achieve toner fixation with a lower electric powder consumption and at a lower temperature.
Besides, there is a tendency for the size of toner particles to be gradually made smaller in order to improve image quality in copying machines and printers. In general, the smaller the solid particles are, the larger the force between the particles is. Similarly, as the resin particles or the toner particles are made smaller, the agglomeration of the particles is more easily brought about.
As a treating apparatus of a continuous processing type using an impact pulverizer, an apparatus as shown in FIGS. 15, 16 and 17 is proposed, which is provided with a cylindrical casing and a rotor 214 having a distributor 220 which is positioned in the casing concentrically with the axis of the casing. A liner 210 set on the internal periphery of the casing 201 is provided with plural grooves in the direction of the rotary shaft 215. The rotor 214 is provided with plural blades 221 made of an abrasion resistance metal and powder material is treated in a treating area 213.
On the upstream side of the casing 201, an inlet 211 for the powder raw material charged through a constant-rate feeder 240 and a vibration feeder 215 and for the incoming air, and a spiral chamber 212 are provided. On the downstream side of the inlet 211, a discharge opening 202 is provided, which is connected to a cyclone dust collector 229 or a bag filter 222 communicating with a suction blower 224. An example of such apparatus is the Turbo Mill crusher manufactured by Turbo Kogyo Co., Ltd.
However such apparatus tends to form particles which are subjected to uneven surface treatment. In addition, even when using cold air flow or a heater and regulating the revolution of the rotor to adjust the level of surface treatment, grinding or re-agglomeration of the solid particles is liable to occur so that the stable surface treatment of the solid particles has been difficult to achieve.
Furthermore, Japanese Patent Application Laid-Open No. 3-56131 (corresponding to U.S. Pat. No. 5,087,546) discloses a continuous mixing apparatus as shown in FIGS. 18 to 22 and a method for producing toner utilizing such apparatus. The apparatus is provided with a cylindrical casing 301, and agitating blades 302 connected to a rotor shaft 304 and fixed blades 303, both set in the casing 301. A disk 313 of the agitating blades 302 is provided with plural blades 312, while annular fixed disk 315 of the fixed blades 303 is provided with plural blades 314.
On the upstream side of the cylindrical casing 301, an inlet 305 for the powder raw material charged through a raw material hopper 307 and a vibration feeder 308 and for the incoming air is formed. On the downstream side of the inlet 305, a discharge opening 306 is provided, which is connected to an external collecting cyclone 309 or a bag filter 310 communicating with a suction blower 311. Such apparatus is used as a continuous mixing apparatus.
However, further improvements have been desired on such apparatus, since it is weak in the impact force of the solid particles against the peripheral wall because of a wide gap between the agitating blades 302 and the side wall of the apparatus, and tends to produce solid particles with uneven surface treatment.